548 PHYSIOLOGY. 



results chiefly o the regulated action of physical and chemical 

 forces. 



The subsidiary operations of vegetation are absorption of food, 

 diffusion or transmission of fluid through the organic structure, assi- 

 milation of absorbed material, and, intimately connected with this, 

 the processes of respiration, transpiration, and metastasis. Secretion 

 is more nearly related to development than to the processes just 

 enumerated. The relations of many of the secretions of plants 

 are very obscure. Starch, chlorophyll, fixed oils, sugar, &c. are of 

 course intimately connected with the vegetative growth ; but we 

 have little clue to the importance, as regards the plant, of the 

 essential oils, resins, alkaloids, &c. 



The Vegetative Propagation of plants presents special modifica- 

 tions connected with the peculiar conditions of organization in the 

 different Classes ; and there are some important considerations 

 connected with the contrasts existing between the results of this 

 and of sexual reproduction. 



The Sexual Reproduction of plants offers a series of phenomena of 

 much interest when viewed comparatively throughout the different 

 great Classes ; and the phenomena of Hybridization and the influ- 

 ence of sexual reproduction in the maintenance of specific characters 

 require especial notice from the vegetable physiologist. 



As the Vegetative propagation is a process of vegetative life trenching 

 on the region of reproduction, so many of the phenomena accompanying 

 sexual reproduction are properly special vegetative actions induced by 

 peculiar stimuli : among these are the phenomena of ripening- of fruits and 

 sporanges, the evolution of heat from flowers, the irritable movements 

 of floral organs, &c. These, and some other unclassed phenomena, will 

 be most conveniently examined apart. In the succeeding Chapters on 

 Physiology we shall examine separately: 1, the processes of Vegetation ; 

 2, the phenomena of vegetative Propagation ; 3, the physiology of sexual 

 Reproduction ; and, 4, various unclassed phenomena met with in a more 

 or less limited range of cases of vegetable life. 



Sect. 2. CELL-LIFE. 



Movements of the Protoplasm, &c. Intimately connected with 

 the early history of the protoplasm of the cell (p. 495) are cer- 

 tain physiological phenomena of the contents of individual cells, 

 which will be most conveniently described here. 



During the time when the protoplasmic contents of young cells 

 are becoming gradually hollowed out into spaces filled with watery 

 cell-sap (p. 494), a regular movement of this protoplasm takes 

 place, which may be observed very readily in young hairs of Phane- 

 rogamic plants (fig. 586), and which probably takes place in an 



